From the U.S. Pat. No. 5,701,121 a system is known comprising an interrogator and a transducer between which information and energy can be transmitted by means of coupled oscillating circuits. The interrogator's magnetic field can be picked up by the transducer to provide energy to an electrical device attached to the transducer. Moreover, data and commands are transmitted between interrogator and transducer by means of modulating the induction field. For transmission from the interrogator to the transducer, i.e. in the direction of energy transmission, amplitude, phase, frequency and pulse modulation are suggested. For transmission in the opposite direction, “power absorption”-signalling is suggested, in which the receiving coil of the transducer is temporarily disconnected, which disconnection is detected at the location of the interrogator by means of monitoring the energy absorption of the energy-transmitting coil.
The international patent publication WO 1994/001846 A1 discloses an electrical connector that comprises of a transformer for inductively transmitting electrical power and information. The connector preferably is integrated into a hinge-joint for the door of a car. Via the connector, electrical power is transmitted from the car to the door to supply a load in the door with electrical energy, and data is transmitted by-directionally. The primary side of the transformer is provided by an H-bridge circuit with a square wave voltage. For transmission of a low frequency signal in the direction of power transmission to drive loud speakers and the door, the pulse of the square wave voltage is HF-modulated. Moreover, information is transmitted in both directions by HF-modulating of the square wave signal, beginning with the rising edges.